Baryon Energy Density Research Articles

Dynamical Explanation of the Dark Matter and Baryon Energy Density Coincidence.

The near equality of the dark matter and baryon energy densities is a remarkable coincidence, especially when one realizes that the baryon mass is exponentially sensitive to UV parameters in the form of dimensional transmutation. We explore a new dynamical mechanism, where in the presence of an arbitrary number density of baryons and dark matter, a scalar adjusts the masses of dark matter and baryons until the two energy densities are comparable. In this manner, the coincidence is explained regardless of the microscopic identity of dark matter and how it was produced. This new scalar causes a variety of experimental effects such as a new force and a (dark) matter density-dependent proton mass.

Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD.

We present a model of cold QCD matter that bridges nuclear and quark matter through the duality relation between quarks and baryons. The baryon number and energy densities are expressed as functionals of either the baryon momentum distribution, f_{B}, or the quark distribution, f_{Q}, which are subject to the constraints on fermions, 0≤f_{B,Q}≤1. The theory is ideal in the sense that the confinement of quarks into baryons is reflected in the duality relation between f_{Q} and f_{B}, while other possible interactions among quarks and baryons are all neglected. The variational problem with the duality constraints is formulated and we explicitly construct analytic solutions, finding two distinct regimes: a nuclear matter regime at low density and a quarkyonic regime at high density. In the quarkyonic regime, baryons underoccupy states at low momenta but form a momentum shell with f_{B}=1 on top of a quark Fermi sea. Such a theory describes a rapid transition from a soft nuclear equation of state to a stiff quarkyonic equation of state. At this transition, there is a rapid increase in the pressure.

Finch–Skea dark energy stars with vanishing complexity factor

We make use of the complexity factor formalism for static and self-gravitating objects, recently proposed by L. Herrera (2018), for setting up a relativistic, anisotropic dark energy stellar model satisfying the vanishing complexity condition. The condition serves as an aid in closing the system of field equations for General Relativity. The popular Finch–Skea ansatz is used for the metric component, grr, with the temporal counterpart determined by imposing the vanishing complexity condition. We assess the physical acceptability of our dark energy stellar model according to the standard requirements for static, spherically symmetric compact matter, and we study the associated matter quantities with respect to the dark energy coupling parameter, α. The effect of α on our stellar model has been studied in detail. It is established that our model is regular and stable, and the radial pressure vanishes at the surface boundary as required by selecting a suitable range for α. We find that the coupling parameter influences the baryonic energy density and pressures; however, the pressure anisotropy remains largely unaffected. This is a novel feature of our dark-energy star model, obtained via the vanishing complexity condition. We further demonstrate the robustness of our model in predicting the observed radii of well-known compact objects such as 4U 1820-30, Vela X-1, LMC X-4, PSR J1614-2230, and PSR J1903+0327 by varying a free parameter arising in the Finck–Skea ansatz. Our findings show that our solution predicts masses beyond the standard general relativity limit of 2.0 M⊙ for neutron stars. The prediction of compact objects with masses in the range of 2.5 M⊙ within our solution-generating framework augers well for the observation of gravitational waves arising in binary mergers.

Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: H0 and S8

Interesting discrepancies in cosmological parameters are challenging the success of the ΛCDM model. Direct measurements of the Hubble constant H 0 using Cepheid variables and supernovae turn out to be higher than inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing surveys consistently report values of the strength of matter clustering σ 8 lower than values derived from the CMB in the context of ΛCDM. In this paper we address these discrepancies in cosmological parameters by considering Dark Energy (DE) as a fluid with evolving equation of state w de(z), constant sound speed squared ĉ s 2, and vanishing anisotropic stress σ. Our w de(z) is derived from the Holographic Principle and can consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus affecting the sound horizon and the comoving angular diameter distance, hence H 0. Here we show DE sound speed plays a part in the matter clustering behaviour through its effect on the evolution of the gravitational potential. We compute cosmological constraints using several data set combinations including primary CMB, CMB lensing, redshift-space-distortions, local distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis we marginalise over ĉ s 2 and find ĉ s 2 = 1 is excluded at ≳ 3σ. For our baseline result including the whole data set we found H 0 and σ 8 in good agreement (within ≈ 2σ) with low redshift probes. Our constraint for the baryon energy density ω b is however in ≈ 3σ tension with BBN constraints. We conclude evolving DE also having non-standard clustering properties [e.g., ĉ s 2(z,k)] might be relevant for the solution of current discrepancies in cosmological parameters.

An asymmetric SIMP dark matter model

In this paper, we construct the first asymmetric strongly interacting massive particles (SIMP) dark matter (DM) model, where a new vector-like fermion and a new complex scalar both having nonzero chemical potentials can be asymmetric DM particles. After the spontaneous breaking of a U(1)D dark gauge symmetry, these two particles can have accidental ℤ4 charges making them stable. By adding one more complex scalar as a mediator between the SIMP DM, the relic density of DM is determined by 3 → 2 and two-loop induced 2 → 2 annihilations in this model. On the other hand, the SIMP DM can maintain kinetic equilibrium with the thermal bath until the DM freeze-out temperature via the new gauge interaction. Interestingly, this model can have a bouncing effect on DM, whereby the DM number density rises after the chemical freeze-out of DM. With this effect, the prediction of the DM self-interacting cross section in this model can be consistent with astrophysical observations, and the ratio of the DM energy density to the baryonic matter energy density can be explained by primordial asymmetries. We also predict the DM-electron elastic scattering cross section that can be used to test this model in future projected experiments.

Cosmological bound on the QCD axion mass, redux

We revisit the joint constraints in the mixed hot dark matter scenario in which both thermally produced QCD axions and relic neutrinos are present. Upon recomputing the cosmological axion abundance via recent advances in the literature, we improve the state-of-the-art analyses and provide updated bounds on axion and neutrino masses. By avoiding approximate methods, such as the instantaneous decoupling approximation, and limitations due to the limited validity of the perturbative approach in QCD that forced to artificially divide the constraints from the axion-pion and the axion-gluon production channels, we find robust and self-consistent limits. We investigate the two most popular axion frameworks: KSVZ and DFSZ. From Big Bang Nucleosynthesis (BBN) light element abundances data we find for the KSVZ axion ΔN eff < 0.31 and an axion mass bound ma < 0.53 eV (i.e., a bound on the axion decay constant fa > 1.07 × 107 GeV) both at 95% CL. These BBN bounds are improved to Δ N eff < 0.14 and ma < 0.16 eV (fa > 3.56 × 107 GeV) if a prior on the baryon energy density from Cosmic Microwave Background (CMB) data is assumed. When instead considering cosmological observations from the CMB temperature, polarization and lensing from the Planck satellite combined with large scale structure data we find Δ N eff < 0.23, ma < 0.28 eV (fa > 2.02 × 107 GeV) and ∑ mν < 0.16 eV at 95% CL. This corresponds approximately to a factor of 5 improvement in the axion mass bound with respect to the existing limits. Very similar results are obtained for the DFSZ axion. We also forecast upcoming observations from future CMB and galaxy surveys, showing that they could reach percent level errors for ma ∼ 1 eV.

Cosmic expansion parametrization: Implication for curvature and H0 tension

We propose an analytical parametrization of the comoving distance and Hubble parameter to study the cosmic expansion history beyond the vanilla $\Lambda$CDM model. The parametrization is generalized enough to include the contribution of spatial curvature and to capture the higher redshift behaviors. With this parameterization, we study the late time cosmic behavior and put constraints on the cosmological parameters like present values of Hubble parameter ($H_{0}$), matter energy density parameter ($\Omega_{m0}$), spatial curvature energy density parameter ($\Omega_{k0}$) and baryonic matter energy density parameter ($\Omega_{b0}$) using different combinations data like CMB (Cosmic microwave background), BAO (baryon acoustic oscillation), and SN (Pantheon sample for type Ia supernovae). We also rigorously study the Hubble tension in the framework of late time modification from the standard $\Lambda$CDM model. We find that the late time modification of the cosmic expansion can solve the Hubble tension between CMB $\&$ SHOES (local distance ladder observation for $H_{0}$), between CMB+BAO $\&$ SHOES and between CMB+SN $\&$ SHOES, but the late time modification can not solve the Hubble tension between CMB+BAO+SN and SHOES. That means CMB, BAO, and SN data combined put strong enough constraints on $H_{0}$ (even with varying $\Omega_{k0}$) and on other background cosmological parameters so that the addition of $H_{0}$ prior from SHOES (or from similar other local distance observations) can not significantly pull the $H_{0}$ value towards the corresponding SHOES value.

Baryogenesis through asymmetric Hawking radiation from primordial black holes as dark matter

We examine the extent to which primordial black holes (PBHs) can constitute the observed dark matter while also giving rise to the measured matter-antimatter asymmetry and account for the observed baryon abundance through asymmetric Hawking radiation generated by a derivative coupling of curvature to the baryon-lepton current. We consider both broad and monochromatic mass spectra for this purpose. For the monochromatic spectrum we find that the correct dark matter and baryon energy densities are recovered for peak masses of the spectrum of $M_{\rm pk} \geq 10^{12}$ kg whereas for the broad case the observed energy densities can be reproduced regardless of peak mass. Adopting some simplifications for the early-time expansion history as a first approximation, we also find that the measured baryon asymmetry can be recovered within an order of magnitude. We argue furthermore that the correct value of the baryon-lepton yield can in principle be retrieved for scenarios where a significant amount of the radiation is produced by PBH decay during or after reheating, as is expected when the decaying PBHs also cause reheating, or when an early matter-dominated phase is considered. We conclude from this first analysis that the model merits further investigation.

Cosmology with recombination spectrum

Precision measurement of the cosmological recombination spectrum can provide an entire new window to look at the early universe. We aim to quantify the information hidden in the cosmological recombination spectrum and for this purpose we have developed a new code following the algorithm proposed in [1,2]. Our code is closely based on the COSMOSPEC [3] code. We find, using Fisher information matrix and assuming that the foregrounds can be subtracted by using higher or lower frequency channels and spatial information, that going beyond the detection will need an experiment with sensitivity 25× better compared to the proposed experiment PIXIE. Such an experiment will be able to measure the cosmological parameters with a precision that is competitive with the CMB anisotropy experiments. The best constrainted parameter is baryon energy density, Ωb, which can be nailed down with incredible precision in principle. We also show that the shape of the hydrogen lines is connected to the speed of the hydrogen recombination, with the peaks of the recombination lines coinciding with the peak of the recombination rate. In general, the shape of the lines encodes information about the rate of recombination as a function of redshift.

The supercooled universe

Strongly-coupled theories at the TeV can naturally drive a long period of supercooling in the early universe. Trapped into the deconfined phase, the universe could inflate and cool down till the temperature reaches the QCD strong scale. We show how at these low temperatures QCD effects are important and could trigger the exit from the long supercooling era. We also study the implications on relic abundances. In particular, the latent heat released at the end of supercooling could be the reason for the similarities between dark matter and baryon energy densities. The axion abundance could also be significantly affected, allowing for larger values of the axion decay constant. Finally, we discuss how a long supercooling epoch could lead to an enhanced gravitational wave signal.

Tighter limits on dark matter explanations of the anomalous EDGES 21 cm signal

We investigate the hypothesis that Coulomb-type interactions between dark matter (DM) and baryons explain the anomalously low 21 cm brightness-temperature minimum at redshift $z\ensuremath{\sim}17$ that was recently measured by the EDGES experiment. In particular, we reassess the validity of the scenario where a small fraction of the total DM is millicharged, focusing on newly derived constraints from Planck 2015 cosmic microwave background (CMB) data. Crucially, the CMB power spectrum is sensitive to DM--baryon scattering if the fraction of interacting DM is larger than (or comparable to) the fractional uncertainty in the baryon energy density. Meanwhile, there is a mass-dependent lower limit on the fraction for which the required interaction to cool the baryons sufficiently is so strong that it drives the interacting-DM temperature to the baryon temperature prior to their decoupling from the CMB. If this occurs as early as recombination, the cooling saturates. We precisely determine the viable parameter space for millicharged DM, and find that only a fraction $({m}_{\ensuremath{\chi}}/\mathrm{MeV})0.0115%\ensuremath{\lesssim}f\ensuremath{\lesssim}0.4%$ of the entire DM content, and only for DM-particle masses between 0.5 MeV--35 MeV, can be charged at the level needed to marginally explain the anomaly, without violating limits from SLAC, CMB, big bang nucleosynthesis (BBN), or stellar and SN1987A cooling. In reality, though, we demonstrate that at least moderate fine tuning is required to both agree with the measured absorption profile and overcome various astrophysical sources of heating. Finally, we point out that a $\ensuremath{\sim}0.4%$ millicharged DM component which is tightly coupled to the baryons at recombination may resolve the current $2\ensuremath{\sigma}$ tension between the BBN and CMB determinations of the baryon energy density. Future CMB-S4 measurements will be able to probe this scenario directly.

Observational constraints on the free parameters of an interacting Bose–Einstein gas as a dark-energy model

Dark energy is modelled by a Bose-Einstein gas of particles with an attractive interaction. It is coupled to cold dark matter, within a flat universe, for the late-expansion description, producing variations in particle-number densities. The model's parameters, and physical association, are: $\Omega_{G0}$, $\Omega_{m0}$, the dark-energy rest-mass energy density and the dark-matter term scaling as a mass term, respectively; $\Omega_{i0}$, the self-interaction intensity; $x$, the energy exchange rate. Energy conservation relates such parameters. The Hubble equation omits $\Omega_{G0}$, but also contains $h$, the present-day expansion rate of the flat Friedman--Lem\^aitre--Robertson--Walker metric, and $\Omega_{b0}$, the baryon energy density, used as a prior. This results in the four effective chosen parameters $\Omega_{b0}$, $h$, $\Omega_{m0}$, $\Omega_{i0}$, fit with the Hubble expansion rate $H(z)$, and data from its value today, near distance, and supernovas. We derive wide $1\sigma$ and $2\sigma$ likelihood regions compatible with definite positive total CDM and IBEG mass terms. Additionally, the best-fit value of parameter $x$ relieves the coincidence problem, and a second potential coincidence problem related to the choice of $\Omega_{G0}$.

Mass in cosmological perspective

We consider the total nonlocal energy associated with a particle at rest in the Hubble flow, i.e., the relational energy between this particle and all connected particles within the causal horizon. The particle, even while at rest, partakes in relative recessional and peculiar motion of connected particles in three dimensions. A geometrical argument due to Berkeley suggests that the nonlocal mass of recessional energy associated with the particle is 3 times its Newtonian mass. It follows that nonlocal recessional and peculiar energy of the Universe are equal, and match Misner-Sharp energy within the apparent horizon. Contributions of recessional and peculiar nonlocal energy are thus shown to generate a 6 times higher level of matter energy than expected from the Newtonian mass. Accordingly, the nonlocal energy density of baryons is expected to be 6 times the standard local energy density of baryons, i.e., ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{b},\mathrm{eff}}=6{\mathrm{\ensuremath{\Omega}}}_{\mathrm{b}}$. At ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{b}}\ensuremath{\sim}0.0484\ifmmode\pm\else\textpm\fi{}0.0017$ [P. A. R. Ade et al. (Planck Collaboration), Astron. Astrophys. 594, A13 (2016) ] this predicts a nonlocal baryon energy density ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{b},\mathrm{eff}}\ensuremath{\sim}\phantom{\rule{0ex}{0ex}}0.290\ifmmode\pm\else\textpm\fi{}0.010$, in agreement with observed matter density ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}\ensuremath{\sim}0.308\ifmmode\pm\else\textpm\fi{}0.012$. The effect of nonlocal mass on solar system and galactic scales is considered.

EXTRACTING HOST GALAXY DISPERSION MEASURE AND CONSTRAINING COSMOLOGICAL PARAMETERS USING FAST RADIO BURST DATA

ABSTRACT The excessive dispersion measures (DMs) and high Galactic latitudes of fast radio bursts (FRBs) hint toward a cosmological origin of these mysterious transients. Methods of using measured DM and redshift z to study cosmology have been proposed, but one needs to assume a certain amount of DM contribution from the host galaxy ( ) in order to apply those methods. We introduce a slope parameter (where is the observed DM subtracting the Galactic contribution), which can be directly measured when a sample of FRBs have z measured. We show that can be roughly inferred from β and the mean values, and , of the sample. Through Monte Carlo simulations, we show that the mean value of local host galaxy DM, , along with other cosmological parameters (mass density in the ΛCDM model, and the IGM portion of the baryon energy density ), can be independently measured through Markov Chain Monte Carlo fitting to the data.

External priors for the next generation of CMB experiments

Planned cosmic microwave background (CMB) experiments will improve what we know about neutrino physics, inflation, and dark energy. The low level of noise, together with improved angular resolution, will increase the signal-to-noise ratio of the CMB polarized data as well as the reconstructed lensing potential of large scale structure. Projected constraints on cosmological parameters are tight, but these can be improved even further with information from external experiments. Here, we examine quantitatively the extent to which external priors can lead to improvement in projected constraints from a CMB-Stage IV (S4) experiment on neutrino and dark energy properties. We find that CMB S4 constraints on neutrino mass could be strongly enhanced by external constraints on the cold dark matter density ${\mathrm{\ensuremath{\Omega}}}_{c}{h}^{2}$ and the Hubble constant ${H}_{0}$. If polarization on the largest scales ($\ensuremath{\ell}&lt;50$) will not be measured, an external prior on the primordial amplitude ${A}_{s}$ or the optical depth $\ensuremath{\tau}$ will also be important. A CMB constraint on the number of relativistic degrees of freedom, ${N}_{\mathrm{eff}}$, will benefit from an external prior on the spectral index ${n}_{s}$ and the baryon energy density ${\mathrm{\ensuremath{\Omega}}}_{b}{h}^{2}$. Finally, an external prior on ${H}_{0}$ will help constrain the dark energy equation of state ($w$).

Fluid dynamic propagation of initial baryon number perturbations on a Bjorken flow background

Baryon number density perturbations offer a possible route to experimentally measure baryon number susceptibilities and heat conductivity of the quark gluon plasma. We study the fluid dynamical evolution of local and event-by-event fluctuations of baryon number density, flow velocity and energy density on top of a (generalized) Bjorken expansion. To that end we use a background-fluctuation splitting and a Bessel-Fourier decomposition for the fluctuating part of the fluid dynamical fields with respect to the azimuthal angle, the radius in the transverse plane and rapidity. We examine how the time evolution of linear perturbations depends on the equation of state as well as on shear viscosity, bulk viscosity and heat conductivity for modes with different azimuthal, radial and rapidity wave numbers. Finally we discuss how this information is accessible to experiments in terms of the transverse and rapidity dependence of correlation functions for baryonic particles in high energy nuclear collisions.

Particlelike solutions in modified gravity: The Higgs monopole

Higgs inflation has received a remarkable attention in the last few years due to its simplicity and predictive power. The key point of this model is the nonminimal coupling to gravity in unitary gauge. As such, this theory is in fact a scalar-tensor modification of gravity that needs to be studied also below the energy scales of inflation. Motivated by this goal, we study in great analytical and numerical detail the static and spherically symmetric solutions of the equations of motion in the presence of standard baryonic matter, called "Higgs monopoles" and presented in 1305.2640. These particlelike solutions may arise naturally in tensor-scalar gravity with mexican hat potential and are the only globally regular asymptotically flat solutions with finite classical energy. In the case when the parameters of the potential are taken to be the ones of the standard model, we find that the deviations from general relativity are extremely small, especially for bodies of astrophysical size and density. This allows to derive a simplified description of the monopole, for which the metric inside the spherical matter distribution can be approximated by the standard metric of general relativity. We study how the properties of these monopoles depend on the strength of the nonminimal coupling to gravity and on the baryonic mass and compactness. An important and original result is the existence of a mechanism of resonant amplification of the Higgs field inside the monopole that comes into play for large nonminimal coupling. We show that this mechanism might degenerate into divergences of the Higgs field that reveal the existence of forbidden combinations of radius and baryonic energy density.

Cosmological Parameters from the Thermodynamic Model of Gravity

Within our recent thermodynamic model of gravity the dark energy is identified with the energy of collective gravitational interactions of all particles in the universe, which is missing in the standard treatments. For a simple model universe composed of neutral and charged particles of identical mass we estimate the radiation, baryon and dark energy densities and obtain the values which are very close to the current cosmological observations.

On the Dynamics of the Ensemble of Particles in the Thermodynamic Model of Gravity

Within the thermodynamic model of gravity the dark energy is identified with the energy of collective gravitational interactions of all particles in the universe, which is missing in the standard treatments. For the model-universe we estimate the radiation, baryon and dark energy densities and obtain the values which are close to the current observations. It is shown that total gravitational potential of a particle from the world ensemble is a scale dependent quantity and its value is twice of Newtonian potential. The Einstein-Infeld-Hoffmann approximation to general relativity was used to show that the acceleration of a particle from the world ensemble can be considered as a relative quantity when the universe is described by the flat cosmological model.

Quantum Field Model of the Origin of Matter-Energy in the Expanding Universe

The model of production of ordinary and dark matter in the decay of a hypothetical anti- gravitating medium in the form of a condensate of (zero-momentum) spinless massive particles, which fills the early universe, is proposed. The decays of these massive particles into baryons, leptons, and dark matter particles are caused by some (after-GUT) interaction with the mass scale between the electroweak and grand unification. The observed dark energy is identified with a portion of a condensate which has not decayed up to the instant of measurement. We show that the mass of dark matter particle being close to 5 GeV and the mass of massive particle of a condensate approximately equal to 15 GeV can be extracted from the WMAP and other astrophysical data about the contributions of baryon, dark matter, and dark energy densities to the total matter-energy density budget in our universe. Such a mass of light WIMP dark matter agrees with the observations of CoGeNT, DAMA, and CDMS. The numerical values of the coupling constant of after-GUT interaction and of the decay rate of massive particle of a condensate, as well as other parameters are obtained.